Intrinsic modeling of radar antennas: from far-field to near-field conditions

We present an intrinsic way for modeling radar antennas operating in near-field conditions for wave propagation in planar layered media. Fundamental antenna features consist of an equivalent set of infinitesimal electric dipoles, field points and associated global reflection and transmission coefficient functions. These antenna characteristic functions permit to describe wave propagation between the radar reference plane and the equivalent source dipoles and field points. Near-field antenna-medium coupling is inherently accounted for and the antenna characteristics do not depend on the medium. We show an example of application in which the dielectric permittivity of a sand subject to a range of water contents is estimated from measurements collected with a vector network analyzer connected to a Vivaldi antenna. A very close agreement between the measurements and the model was obtained and the retrieved permittivities were very well consistent with the corresponding water contents. The proposed method shows great promise for digital soil mapping using ground-penetrating radar (GPR) and non-destructive testing of materials.